I'm not cryptography expert (well, I'm here after all!) but I have this doubt…
Suppose I have 2 different keys:
And a plain text:
If I use AES128 on my plain text with my first key I get this:
now, if I use on this cipher text my second key I got this:
Looks pretty safe, but I have a doubt: does this have the same security of a AES256? Or a single 128bit key that can decode my final text can exists?